1. Field of the Invention
The present invention relates to injection molding machines and to die closing units for the latter, and more particularly to a die closing unit for an injection molding machine whose molding die has multiple transfer sections for the production of articles with embedded insert parts, whereby the transfer sections of the injection molding die are alternatingly removable from the open die for the placement thereinto of insert parts, as another transfer section is involved in an injection molding cycle.
2. Description of the Prior Art
The idea of devising the injection molding die of an injection molding machine to comprise at least two transversely interchangeable identical transfer sections is not new. A known version of such a die closing unit includes a transfer platen carrying the transfer sections of the injection molding die between a loading station located laterally outside the die closing unit itself and a closing station in which the transfer section is aligned with the other die section, or sections, for a closing motion by the die closing unit. In this case, however, the transfer platen itself is subjected to the closing pressure exerted by the die closing unit, meaning that the transfer platen has to be strong enough to withstand that closing pressure, which may reach many tons.
One shortcoming of this prior art arrangement is, accordingly, that the transfer platen has to be comparatively heavy. Since the prior art transfer platen in question is of the reciprocating type, moving along a straight line between a loading station and a closing station, the drive for this reciprocating motion must be correspondingly powerful, in order to overcome the high inertia of the massive transfer platen. On the other hand, the speed of the platen drive is limited, due to the fact that the mass of the moving parts, if stopped and started too rapidly, would create undesirable deflections and vibrations in various component parts of the die closing unit.
An additional shortcoming of this prior art structure relates to the fact that the transfer sections of the injection molding die are moved along a straight line into and out of the closing station, so that the respective loading stations have to be located on opposite sides of the closing station. This means that the operator in charge of placing insert parts into the transfer sections in the loading stations, is obliged to move from station to station on opposite sides of the die closing unit. Alternatively, a separate operator is required for each of the two loading stations.